An acceleration estimation device for a vehicle is known in the art which estimates an acceleration produced on a vehicle using, for example, a digital differentiation method wherein a variation of vehicle speed is found from a past vehicle speed signal and a current vehicle speed signal.
This acceleration estimation device is used for example in a transmission controller of a continuously variable transmission. The transmission control determines the gradient of a road, such as a flat path or a downhill slope, from the estimated acceleration and a throttle opening, and a speed change ratio according to traveling conditions is applied.
However, in this acceleration estimation device, there is some noise in the vehicle speed signal due to the effect of computational error or the road surface even when the vehicle is traveling at constant speed. When, for example, the period of estimating the acceleration is 10 milliseconds and the vehicle speed signal fluctuates by .+-.0.1 Km/hr, a maximum error of 0.566 G occurs in the estimated acceleration. This error considerably affects the control precision of the speed change controller.